The present invention relates to the construction of pre-stressed structures from prefabricated matched concrete elements.
The invention applies in particular, but not exclusively, to bridges built by cantilevered construction with prefabricated segments having matched coupling surfaces (see for example the article: xe2x80x9cEvolution et recents developpements des ponts a voussoirs prefabriquesxe2x80x9d (xe2x80x9cEvolution and recent developments of bridges made of prefabricated segmentsxe2x80x9d) by Jacques Mathivat, Annales de l""lnstitut Technique du Batiment et des Travaux Publics, Supplement to No. 342, September 1976, pages 21xe2x80x9432, or the patent application EP-A-0 462 350).
In this technique, the successively assembled elements (segments) of the bridge are manufactured one after the other, the front face of the element n serving to delimit the rear side of the manufacturing mold of the element n+1. This guarantees the matching of the adjacent faces of the elements to be assembled. These faces are glued one on the other during the placing of the element n+1 on the building site. Complementary raised parts are usually provided on these faces to facilitate their mutual positioning and to help to support the element n+1 before its definitive fixing.
These structures are frequently subjected to a longitudinal pre-stress by means of pre-stressing cables threaded in sheaths embedded in the concrete of several successive elements.
Carrying out this pre-stress is a delicate operation.
The positioning of the sheath sections in the elements must be very precise so that the pre-stressing cables can be threaded without difficulty.
To guarantee the sealing of the sheath at the interfaces between elements is the most difficult. This sealing is necessary to ensure the durability of the pre-stressing subjected to the risks of infiltrations at the level of the joint between the elements. The joint can be made according to two processes: xe2x80x9cdry jointxe2x80x9d when the concrete faces are placed side by side without any interface product; or xe2x80x9cglued jointxe2x80x9d when an interface adhesive is placed at the level of the joint. In this second case, the sealing also fulfils the necessity of avoiding the epoxy or similar adhesive placed between the elements being able to penetrate into the sheaths and hinder the introduction of the cables. On the other hand, the sheaths are generally injected with a filling product (cement grouting, grease, wax, resin, etc) serving in particular to protect the cables against corrosion. This product must not escape to the outside of the sheath during the injection.
Certain zones of the structure may have a rather large density of sheaths, and there is not the assurance that the epoxy adhesive will achieve the sealing between these sheaths. The result is the grave risk that grouting injected under pressure into the sheath may infiltrate into one or several neighboring sheaths, where the injection then becomes very difficult, or even impossible.
In general, pneumatic tests are carried out to check the sealing of the pre-stress sheaths before installing the cables and injecting the grouting. If leaks are detected between some sheaths, it is necessary to inject the grouting very carefully in a way to attempt to have a single advancing grouting front in these different sheaths. The resulting injection procedures are extremely complicated and very difficult to control.
The solutions consisting in interposing O rings around the sheaths between the interconnected faces of the elements are not reliable in terms of sealing, these seals being able to be displaced during the positioning of the element n+1.
The patent application FR-A-2 596 439 describes a connection device between pre-stress sheath sections, comprising a cylindrical sleeve engaged between the mouths of two contiguous sections to ensure the continuity of the sheath, and a resilient seal surrounding the cylindrical sleeve to carry out the sealing and to compensate for the positioning irregularities of the units and their dimensional differences.
It has also been proposed to introduce a longitudinally pleated sleeve into the sheath after the gluing, this sleeve being brought at the level of the previously assembled contact surfaces then expanded with the aid of a pneumatic device in order to be glued to the internal wall of the sheath by means of an adhesive placed at the bottom of the pleats. This method involves a very complex implementation, moreover impossible when the sheaths are not rectilinear. Moreover, it does not prevent the infiltrations of adhesive into the sheath during the assembly of the elements.
An object of the present invention is to propose a simple and efficient solution to the problems encountered when carrying out the pre-stressing of structures constructed from matched prefabricated elements.
The invention thus proposes a process of manufacturing concrete construction elements including at least first and second matched elements, the process including the steps of:
placing in a mold at least one first pre-stress sheath section having an end connected to a first sleeve applied against a wall of the mold, the first sleeve having an internal shape engaging a positioning boss placed on said wall;
pouring concrete into said mold so as to obtain the first element after setting of the concrete;
extracting from the mold the first element, one contact face of which has been shaped by said wall;
constructing a second mold one side of which consists of said contact face of the first element;
placing in the second mold at least one second pre-stress sheath section having an end connected to a second sleeve held in position relative to the first sleeve by means of a positioning joint resiliently held in at least one of the first and second sleeves;
pouring concrete into the second mold so as to obtain the second element after setting of the concrete; and
extracting the second element from the second mold, by disengaging the positioning joint from at least one of the first and second sleeves.
The positioning joint may be the same piece as the joint which will achieve the sealing between the sleeves after the definitive assembly of the elements. In this case, the joint can be left in place in one or other of the two sleeves during the storage of the elements.
The sleeves and the joint ensure a precise and correct positioning of each section of sheath in each element, as well as the good alignment of successive sections. The dimensional differences to be compensated are thus minimized.
During the assembly of two consecutive elements, the sealing joints, with which the sleeves terminating the sheath sections on the face of one of the elements are provided, engage the sleeves ending the corresponding sheath sections of the other element. This engagement provides the sealing of the sheath in relation to the adhesive, with which one of the complementary faces is generally coated. It ensures moreover the absence of communication with the outside or between neighboring sheaths during injection of the cement grouting or other filling product into the sheaths.
The sealing joint may be integral with one of the two sleeves. But it is preferably fixed in a removable manner on one of the two sleeves, for example by screwing or by resilient fitting.
In preferred embodiments, the process of manufacturing concrete construction elements according to the invention has one or other of the following features:
the positioning boss may be provided with resilient coupling means which engage with an annular groove present in the internal shape of the first sleeve in order to hold it in a removable manner in the mold;
the sleeve in which the positioning joint is resiliently held may have an angular opening of at least 30 degrees;
the positioning joint may be resiliently held in each one of the first and second sleeves;
the positioning joint may be screwed in one of the first and second sleeves;
when a feature according to one of the two previous paragraphs is provided, the positioning joint may have an orifice coaxial with the sleeves, extending therethrough, said orifice having a cross-section at least equal to the internal cross-section of the first and second sheath sections, and in this case the positioning joint is left in place in the first or the second sleeve after the extraction of the second element.
The invention is also intended for a construction work comprising an assembly of prefabricated elements of a series of elements such as defined above, the contact faces of the matched elements being applied one against the other so that the sheath sections are placed in the extension one of the other to form completed sheaths, with joints engaged in the sleeves in order to connect in a sealed manner the adjacent sheath sections, and wherein pre-stressing cables and a filling product occupy the interior of the sheaths.